The present invention concerns a multi-function watch provided with a time keeping microcomputer.
U.S. Pat. No. 4,063,409 discloses a watch of this kind, wherein the microcomputer comprises a data memory in the form of a random access memory, combined with a programmable logic unit. An oscillator supplies an internal time base and controls the circuits which operate on the data in the random access memory. The clock and control circuits comprise a program memory in the form of a read only memory, which permits reading and handling in accordance with a given program of the data contained in the data memory. The programmable logic unit selects data from the data memory, increments such data, compares the data to limit values and actuates one or more gates in accordance with the desired program. Such data may be selectively displayed, for example by means of a liquid crystal display. The functional and display modes of the microcomputer may be adapted to the functions desired in a specific multi-function watch, by suitably modifying the programmable logic unit and the program memory, without altering the design lay-out of the system.
The main disadvantages of such a microcomputer watch are as follows:
a. Computation of time must be repeated at a rate which depends, in particular in the chronograph mode of operation, on the precision of the chronograph. If the precision of the chronograph is to be one tenth of a second, that represents a rate which is ten times that of normal operation, and therefore involves a very high level of consumption.
b. The time required to perform the successive operations relating to time computation is of the order of 20 milliseconds. It is therefore not possible to effect chronographic time measurement to a hundredth of a second, with the full degree of reliability desired.